Single crystal growing method having improved melt control

ABSTRACT

In a single crystal growing technique (crystal pulling) a method for minimizing impurity contamination and preventing heat convection currents from affecting the solid-melt crystal growing interface which uses a floating baffle plate in the interior of the feed melt containing crucible in order to obtain a single crystal of a compound semiconductor having a high melting point and exhibiting a high dissociation pressure at said melting point such as a compound semiconductor of Groups III-V, especially GaAs or Gap, the crystal having a small dislocation density. Improvement is made on the shape of the baffle plate and on baffle plate control mechanisms, and this baffle plate is combined with selected intra-furnace pressure or heating mechanisms or temperature measuring mechanisms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single crystal growing method andapparatus suitable for use in pulling a crystal from a melt of acompound semiconductor of elements of Groups III-V, especially galliumarsenide (GaAs), according to the Czochralski method.

2. Description of the Prior Art

For compound semiconductors of the type noted to fully exhibit theirintrinsic optical and electrical characteristics, it is necessary thatthe single crystals prepared have a high purity and a high perfectnessof crystal.

Compound semiconductors of elements of Groups III-V such as GaAs,gallium phosphide (GaP) and indium phosphide (InP) melt as high as 1238°C., 1470° C. and 1050° C. and exhibit high dissociation pressures (0.9,30 and 15.5 atm respectively) at such melting points. Growing thesecompound semiconductors according to the known crystal pulling methodsis extremely difficult.

Single crystals of GaAs are in increasing demand because they exhibitlarger electron transfer than silicon (Si) when compared on a size ordimensional basis. Presently, the method used to obtain such GaAs singlecrystal is the well known horizontal Bridgman method. This method hasthe drawback that contamination may be caused by impurities diffused ortransferred to the GaAs as the single crystal made is being supported bya quartz board or a quartz sealed tube. Also, according to this knownmethod, the sectional shape of a grown crystal is not circular and thisis a disadvantage. Recently, because of these technical problems anddifficulties, various efforts have been made to try to grow such singlecrystals according to the Czochralski method.

According to the well known Czochralski method, in principle, a singlecrystal of a higher purity can be obtained than what is obtainableaccording to the horizontal Bridgman method. In the case of GaAs inparticular, and also GaP and InP, a technical problem still existsconcerning the perfectness of crystals obtainable. Thus, research iscontinuously being made searching for a way to obtain crystals of suchmaterials characterized by a smaller dislocation density.

Those skilled in this art well know and appreciate that the presence ofexcessive dislocations or a large dislocation density cause theelectrical and optical characteristics of a semiconductor device madefrom these single crystals to be deteriorated or to show an abnormality.

Such dislocations are sometimes created during the device manufacturingprocess, but in most cases are present from the beginning in GaAs singlecrystal used as a substrate for manufacturing a device. The dislocationspresent in the substrate are caused mainly by a heat distortion duringproduction of the single crystal, and this heat distortion is sometimescaused by an abrupt temperature gradient in the interior of the crystalinduced by a convection current of an inert gas which is being used toestablish an inert atmosphere of a high pressure in the crystal growingfurnace. One major cause of dislocations is considered to be anynon-uniform temperature distribution at the solid-melt interface causedby a heat convection current which occurs in the feed melt.

To prevent such heat convection, it is already known to float a heatconvection preventing plate in a position below the surface of the feedmelt when pulling a single crystal, the heat convection preventing platehaving a diameter somewhat larger than that of the single crystal beinggrown but fairly smaller than that of the crucible containing the feedmelt. This technique is effective against a heat convection currenttravelling from the center toward the outside in the feed melt, but isnot always fully effective against a heat convection current travellingfrom the outside toward the center.

Further, it is known to float a convection preventing plate in aposition below the surface of a feed melt by virtue of its buoyancy, theconvection preventing plate having a diameter larger than that of thesingle crystal being pulled and somewhat smaller than the insidediameter of the crucible, and to conduct the feed melt upwardly beyondthe convection preventing plate through fine holes formed in the plateor through a gap formed between the outer periphery of the convectionpreventing plate and the inner periphery of the crucible. But, when thefeed melt is viscous, it does not pass smoothly through the fine holesand/or the gap, thus, slowing down the pulling operation and therebyincreasing the time required to grow a crystal. Also, if carelessnessresults in a deficiency of the feed melt in the single crystal pullingregion, this would cause great difficulties.

Further causes of dislocation are heat radiation from a liquid sealingagent such a B₂ O₃ which is often used to cover the upper surface of afeed melt, and heating differentials resulting from lowering of the feedmelt level in the crucible as the crystal growth proceeds and areespecially evident at the end of the single crystal pulling operationwhen the conditions are substantially altered from those at thebeginning of the operation. The crucible plays the role of a heatretaining cylinder as the single crystal pulling operation progresses,thus making effective temperature control (control of a constanttemperature gradient) extremely difficult.

At present, the internal temperature of a crucible containing feed meltis merely estimated by a thermocouple disposed outside the crucible. Butfrom the above discussion, one can readily appreciate that such anarrangement is a coarse control and quite insufficient andunsatisfactory as a temperature measuring means for pulling a singlecrystal of a compound semiconductor as noted above. In such a case, thepulling operation requires the prevention of temperature variationswhich cause a heat distortion and providing and making an exact control.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a singlecrystal growing method and apparatus capable of obtaining a crystal of ahigh purity and a small dislocation density when produced according tothe general teachings of the Czochralski method, the particular singlecrystal having a high melting point and exhibiting a high dissociationpressure at its melting point, such as a compound semiconductor ofelements of Groups III-V.

It is a secondary object of the present invention to provide a singlecrystal growing method and apparatus in which heat convection currentsof a feed melt can be completely prevented from affecting the singlecrystal pulling operation or the solid-melt interface, and the feed meltcan be fed smoothly onto the solid-melt interface without excess ordeficiency through a gap formed between the outer periphery of a baffleplate and the inner wall of the crucible containing the feed melt.

It is a further object of the present invention to provide an apparatuscapable of measuring temperature extremely accurately and of controllingaccurately the temperature of those portions of the crystal growingoperation which require an accurate temperature control, such as thefeed melt, the solid-melt interface region and the liquid sealing agentregion.

According to the present invention, in order to achieve theabove-mentioned technical objects when pulling a single crystal from afeed melt, a baffle plate, having an outside diameter somewhat smallerthan the inside diameter of a crucible and also having a feed meltguiding portion at least on its outer periphery, is floated verticallymovably in a predetermined position below the surface of the feed melt,and is maintained at a predetermined spacing from the surface of thefeed melt while the crucible and/or the baffle plate are rotated duringthe single crystal pulling operation.

Moreover, in order to prevent impurity contamination, the baffle plateis formed of alumina (Al₂ O₃), silicon nitride (Si₃ N₄), BN (boronnitride) or PBN (pyrolytic boron nitride). A molybdenum heater is usedto heat the crucible and the feed melt.

Further, the baffle plate is held in proper position by being presseddown from above or by being fixed to a plurality of moving rods whichare suspended vertically axially movable. Thus, the baffle plate can bemaintained in its predetermined position as the feed melt lowers. Also,the baffle plate can be held in set position and the crucible moved upand down.

According to the present invention, moreover, in pulling a singlecrystal by the liquid encapsulated method, the interior of the furnacecontaining the crucible and feed melt is held in at high pressure and inan inert gas atmosphere; a baffle plate is floated in a predeterminedposition below the surface of the feed melt; a control is provided tomaintain the predetermined spacing between the baffle plate and the feedmelt surface during the single crystal pulling operation; and aplurality of heating means are coaxially provided around the cruciblewith the plurality of heating means being each controlled independently.

According to the present invention, moreover, in pulling a singlecrystal from a feed melt, there are provided a plurality of heatingmeans and axially movable temperature measuring means. The plurality ofheating means are each controlled independently in accordance with adetected signal provided from the temperature measuring means whichmeasures the temperature of preselected regions or points in thecrucible and/or the melts contained in the crucible.

Further, according to the present invention, when floating a baffleplate in the feed melt contained in the crucible, a temperaturemeasuring means is enclosed or otherwise provided for in a single orplural moving rods which support or hold the baffle plate.

Moreover, the single crystal pulling apparatus of the present inventioncomprises a pressure- and heat-resistant electric furnace, a singlecrystal pulling shaft which is driven non-invasively within the electricfurnace such as by a magnetic mechanism, a feed melt holding crucibleplaced and fixed on the upper portion of a crucible supporting rod whichis also driven non-invasively within the electric furnace such as by amagnetic mechanism, a liquid sealing agent floated on the surface of thefeed melt in the crucible, a baffle plate held in a predeterminedposition below the feed melt surface, means for maintaining thepredetermined spacing between the baffle plate and the feed melt surfacewhile pulling a single crystal, a plurality of heating means mounted inan axially vertically arranged fashion around the outside of thecrucible, and means for controlling the plurality of heating means eachindependently.

Under the construction described above of the invention, a heatconvection current created in the feed melt will be prevented fromdisturbing or affecting the solid-melt interface, and the temperaturedistribution at this particular area will be rendered flat and uniform.Also, it is possible to prevent heat radiation through the liquidsealing agent. Further, the temperature of the feed melt, the solid-meltinterface or the liquid sealing agent can be measured directly andaccurately during the single crystal pulling operation, and bycontrolling the plural heating means in accordance with detectedsignals, it is possible to make an accurate temperature control withlittle temperature variation and thereby minimize the occurrence of aheat distortion, so that the dislocations that would otherwise be causedby such heat distortion are prevented and a single crystal of anextremely small dislocation density can be obtained. Also, the impuritycontamination of the crystal can be minimized.

In the present invention, moreover, by holding the furnace interior at ahigh pressure under an inert gas atmosphere, it is possible to preventthe dissipation of a volatile component, and even though such highpressure inert gas atmosphere is present, gas-tightness (hermetic seal)can be ensured completely, under which condition a smooth movement ofthe drive system is ensured. Further, the baffle plate can be held in apredetermined extremely stable position in the crucible during thesingle crystal pulling operation.

The above and other objects, features and advantages of the inventionwill become clear from the following description of the preferredembodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrative of the present invention;

FIG. 2 is a perspective view of a baffle plate;

FIG. 3 is a view illustrative of temperature gradient and temperaturevariation;

FIG. 4 is a schematic view illustrating another embodiment of theinvention;

FIG. 5 is a schematic view illustrating an advanced state of pulling ofa single crystal; and

FIG. 6 is a schematic view illustrating a further embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIGS. 1 and 3, the reference numeral 1 denotes apressure- and heat-resistant electric furnace of a completely closedhermetically sealed structure with thin-walled cylinders 2 and 3centrally projecting axially vertically therefrom. The electric furnace1 is made of stainless steel, for example. In the lower cylinder 2 isenclosed gas-tightly a crucible supporting rod 6, with a verticalmovement drive mechanism 4 and a rotation drive mechanism 5 beingdisposed therearound, both drive mechanisms 4 and 5 utilizing a magneticforce. For drive mechanisms 4 and 5 may be used those drive mechanismswhich are disclosed in my copending application Ser. No. 675,404 filedeven date hereof, now U.S. Pat. No. 4,569,828, entitled "Crystal PullingApparatus for Making Single Crystals of Compound SemiconductorsContaining a Volatile Component." On the upper end portion of thecrucible supporting rod 6 is fixed a crucible 7 comprising an outercrucible 7a formed of, for example, graphite and an inner crucible 7bformed of, for example, quartz.

In the upper cylinder 3 is enclosed gas-tightly a single crystal pullingrod 8 with a vertical movement drive mechanism 10 and a rotation drivemechanism 9 being disposed therearound, both drive mechanisms 10 and 9utilizing a magnetic force. For drive mechanisms 9 and 10, the onesdisclosed in the aforementioned copending application may be used.Outside the crucible 7 are coaxially disposed a heating means 11comprising heaters 11a, 11b, 11c and 11d which are controlledindependently of one another and which are formed preferably ofmolybdenum. The heaters 11a, 11b, 11c and 11d are controlledindependently in accordance with a signal provided from a thermocouple(not shown) by means of a conventional temperature control box 19 sothat a predetermined temperature gradient is created in which the higherthe position or location in the crucible, the lower the temperature. Inthe crucible 7 is contained a feed melt 12, e.g. GaAs, the upper surfaceof which is covered with a liquid sealing agent 13, e.g. B₂ O₃. In theillustrated embodiment, a GaAs single crystal 15 is being pulled bymeans of a seed crystal 14 attached to the lower or fore end of thesingle crystal pulling rod 8. The crystal I5 is pulled through theliquid sealing agent 13.

In a predetermined position below the surface of the feed melt 12 isfloated an unperforated baffle plate 16 (best shown in FIG. 2) by beingheld down by three movable or control rods 18 which contact or engagethe upper surface of baffle plate 16 and which are suspended from abovethe crucible 7, the baffle plate 16 having an outside diameter somewhatsmaller than the inside diameter of the crucible 7. The baffle plate 16is held down through the control rods 18 by a force equal to thatnecessary to counterbalance the bouyancy of the baffle plate andmaintain the same at the predetermined position (or spacing) from thesurface of the feed melt as the crystal 15 is grown. The baffle plate16, as shown in FIG. 2, has an upturned flange about its periphery whichis cut out at spaced intervals to form a scalloped edge. The flangedefines feed melt guiding portions 16a which appear as a wavy unevennesson the upper surface of its outer periphery. Baffle plate 16 is formedof Al₂ O₃, Si₃ N₄, BN, or PBN. The moving rods 18 are formed of BN, forexample. These three moving rods 18 are suspended from cylinders 20which are vertically erected on the electric furnace 1 radially spacedabout cylinder 3 so as to constitute a regular triangle with the uppercylinder 3 as the center. Cylinders 20 like cylinders 2 and 3 andfurnace 1 are all hermetically sealed. The thus-suspended moving rods 18are adapted to be vertically moved simultaneously by means ofnon-invasive drive mechanisms 21 which utilizes, for example, a magneticforce. Such an arrangement is disclosed in my copending application Ser.No. 674,410 filed even date herewith, now U.S. Pat. No. 4,721,601 andentitled "Apparatus for Positioning and Locating a Baffle Plate in aCrucible."

Thus, the moving shafts such as the crucible supporting rod 6, singlecrystal pulling rod 8 and control rods 18 are driven by the non-invasivedrive mechanisms utilizing, for example, a magnetic force, so even whenthe interior of the electric furnace 1 is filled with an inert gas of ahigh pressure, the gas-tightness of the furnace is fully maintained andthe rods and shafts can be moved smoothly in the high pressureatmosphere.

Further, since the outside diameter of the baffle plate 16 is a littlesmaller than the inside diameter of the crucible 7, a heat convectioncurrent in the feed melt 12 occurring below the baffle plate 16 andadvancing from the center toward the outside, as well as a heatconvection current advancing from the outside toward the center, will beobstructed by the baffle plate 16 and have no influence upon the uppersurface of the baffle plate 16. Consequently, as shown in FIG. 3, thetemperature of the solid-melt interface region above the upper surfaceof the baffle plate 16 is extremely more stable in comparison with whatit would be were the baffle plate not used.

Further, by holding the heaters 11a, 11b and 11c at 1400° C. and theheater 11d at 1200° C., as shown also in FIG. 3, the temperature ishigher by 30° C. in a lower position of the crucible and lower by 30° C.on the upper surface of B₂ O₃ than would be the case in the absence ofthe baffle plate 16. Thus, the single crystal being pulled is betterable not to be thermally distorted by the radiation heat from B₂ O₃.

Further, in the case where the feed melt guiding portions 16a are formedon the upper surface of the outer periphery of the baffle plate 16, theguiding portions 16a comprised of alternate projections and cut outsfunction to roll in and draw up the feed melt 12 from the lower surfaceto the upper surface of the baffle plate 16 through a gap (a) withrotation of the baffle plate 16 or the crucible 7, whereby the feed melt12 can be fed always smoothly to the solid-melt interface region abovethe baffle plate 16 without excess or deficiency. In this respect, asuperior effect is exhibited as compared with the construction in whichthe feed melt is passed through fine holes formed in the baffle plate 16itself or through a gap formed between the outer periphery of a flatbaffle plate and the inner wall of the crucible.

Further, since the guiding portions 16a function to guide the feed meltfrom the outer periphery of the crucible 7 to the solid-melt interfaceregion on the upper central portion of the crucible 7, the temperatureof the guided feed melt falls a little in the meantime so that thetemperature distribution of the solid-melt interface region can beprevented from experiencing distortion.

Further, since the guiding portions 16a function to stir the feed melton the baffle plate 16, the growth of the single crystal is sped up.

The guiding portions 16a may be constituted by plural openings which areformed in the upstanding periphery wall of the baffle plate 16. Theguiding portions 16a also may be constituted by plural openings or wavyunevenness formed in a radial direction of the baffle plate 16. Theplural openings and the wavy unevenness may be shaped or tapered or bentedges or fins for cutting the feed melt.

It has been discovered that by using molybdenum wires as the heaters11a, 11b, 11c and 11d, the impurity contamination from the wire heatersis minimized.

The baffle plate 16 may be fixed to the lower or fore end of the controlrods 18, or only a single rod 18 may be used. In the case of fixing thebaffle plate 16 to the rods 18, there is the advantage that the baffleplate 16 can be used repeatedly. If a peep glass is used for thefurnace, a baffle plate fixed to a rod 18 and withdrawn to a certainposition, such as raised before heating is commenced, may obstruct theview of the peep glass.

A GaAs single crystal was pulled as follows using the apparatusillustrated in FIGS. 1 and 3.

First, into the crucible 7 having an inside diameter of 90 mm and adepth of 100 mm was placed 1,700 g of polycrystalline GaAs, then 300 gof B₂ O₃ was placed thereon. The baffle plate 16 formed of BN was put onthe upper surface of the B₂ O₃.

Then, the crucible 7 was placed inside the heating means 11 and theinterior of the furnace 1 was vacuum evacuated. Thereafter, the interiorof the furnace 1 was pressurized to 100 atm with argon as the inert gas,and the temperature of the heaters 11a, 11b and 11c raised to 1400° C.,while that of the heater 11d was raised to 1200° C., to melt the GaAs.B₂ O₃ was the first to melt and then the GaAs polycrystalline materialmelted and the baffle plate 16 floated on the feed melt 12 below the B₂O₃ which became about 11 mm (m/m) in thickness due to its specificgravity. This melted state was confirmed through a peep glass (notshown) and the rods 18 were moved down to immerse the baffle plate 16into the feed melt 12 to a position in which the spacing between theupper surface of the baffle plate 16 now located below the surface ofthe melt and the lower surface of B₂ O₃ was about 17 mm.

Then, the single crystal pulling rod 8 was moved down to immerse theseed crystal 14 attached to its lower or fore end into the feed melt 12through the B₂ O₃ layer, and the rod 8 was rotated at a rate of about 8r.p.m. to have the seed crystal contacted thoroughly with the feed melt12, while the crucible was rotated in the opposite direction also at arate of 8 r.p.m. The single crystal was pulled in the direction of [111]at a rate of about 15 mm/hr. During this pulling operation, the baffleplate 16 was moved down by the rods 18 to maintain its predeterminedposition below the surface of the feed melt 12.

The GaAs single crystal thus obtained was 50 mm in diameter and 150 mmin length, and its etch bit density was 1.2×10⁴ cm⁻² at the portion 10mm from the outer periphery, 4.2×10³ cm⁻² at 15 mm from the outerperiphery and 6.7×10⁴ cm⁻² at 20 mm from the outer periphery. Defectssuch as dislocations were scarcely recognized in this single crystal,and thus, the single crystal growing method of the present inventionproved to be very superior even in comparison with the horizontalBridgman method.

Although the above example concerns pulling a single crystal of GaAs, itgoes without saying that the process of the present invention is alsoapplicable to the pulling of single crystals of other compoundsemiconductors such as, for example, GaP and IaP and perhaps may havesome applicability to pulling crystals of Si and Ge.

The baffle plate may be held down from above my control rods 18 or,alternatively, the baffle plate and the rods may be integrally fixed toeach other. The former possibility is advantageous in that since thebaffle plate is enclosed beforehand in the crucible, it is not anobstacle to viewing through a peep glass no matter in which position thepeep glass is located, but has the disadvantage that the baffle plateremains in the crucible and solidifies together with the residual feedmelt, thus running to waste at every manufacturing process. On the otherhand, the latter possibility is disadvantageous in that since the baffleplate must be pulled up outside the crucible before melting, the viewthrough the peep glass may be obstructed in some particular positionthereof, but has the advantage that the baffle plate can be usedrepeatedly because it can be pulled up outside the crucible aftercompletion of the single crystal pulling operation.

Further, it has been found that where the baffle plate is of a smalldiameter and a large thickness and the control rod is thick and strong,only one rod may be used. Where the baffle plate is thin and the rod isnot so thick, it is desirable to use plural rods, or else the supportfor the baffle plate becomes unstable.

Referring now to FIGS. 4 and 5, there is illustrated another embodimentof the present invention, in which the numeral 22 denotes an electricfurnace and the numeral 23 denotes a heating means comprising, forexample, axially quartered heaters 23a, 23b, 23c and 23d. Inside theheating means 23 is disposed a crucible 25 fixed on a cruciblesupporting rod 24 which is inserted gas-tightly into the furnace 22rotatably and vertically movably in the manner previously explained. Thecrucible 25 comprises an outer crucible 25a formed of, for example,graphite and an inner crucible 25b formed of, for example, quartz, andit contains a feed melt 26 which is GaAs, for example. On the uppersurface of the feed melt 26 of GaAs, a liquid sealing agent 27 such asB₂ O₃ is kept floating due to its specific gravity. From above thecrucible 25 is suspended a rotatable and vertically movable (asdescribed) single crystal pulling rod 28 gas-tightly through the furnace22, and from a seed crystal 29 attached to the lower or fore end thereofis growing a single crystal 30 whose lower or fore end is immersed inthe feed melt 26 through the liquid sealing agent 27.

A protective tube 32 formed of, for example, BN with a temperaturemeasuring means 31 such as a thermocouple or the like enclosed thereinis suspended from above into the furnace vertically movably (asdescribed) and is situated between the single crystal 30 being pulled upand the inner wall of the crucible 25, with its lower or fore endimmersed into the feed melt 26. A temperature signal detected by thetemperature measuring means 31 is displayed on an indicating meter 33aand at the same time it is fed to a conventional temperature controller33, whereby the heaters of the heating means 23 are controlled eachindependently.

Before the feed melt 26 is prepared, the protective tube 32 is pulled upabove the crucible 25, and after preparation of the feed melt 26, thetube 32 is moved down to measure the temperature of the solid-meltinterface region to know the temperature suitable for crystal pullingexactly, and to control the temperature at which the seed crystal 29 isimmersed and pulled up. During the pulling operation, the protectivetube 32 is moved up and down by any known means (such as describedearlier) to measure the temperature of any accessible point in thecrucible to ascertain the temperature of, for example, the feed melt 26,solid-melt interface 34 and liquid sealing agent 27. The detectedtemperature signals are fed to the temperature controller 33 to adjustthe temperature of the heating means 23. Even when the liquid level inthe crucible lowers with advancement of the single crystal pullingoperation as shown in FIG. 5, it is possible to pull the single crystalwith little temperature variation under an exact temperature controlscarcely different from that at the beginning of the pulling operation.

Referring now to FIG. 6, there is illustrated a further embodiment ofthe present invention, in which a baffle plate 36 for preventing heatconvection is floated in a feed melt 35, and a plurality of rods 37formed of, for example, BN, are used to hold the baffle plate 36suspended vertically axially movably in crucible 38. In each of the rods37 is enclosed a temperature measuring means 39 comprising athermocouple, for example, which is spatially located with respect tothe baffle plate 36, that is, is located spaced from the end of rod 37to be in position to measure the temperature at a preselected point orregion in the feed melt, crucible or liquid sealing layer.

This arrangement is advantageous in that the temperatures of pluralregions in the crucible 38 can be measured at the same time whereby amore exact temperature control can be effected. In this embodiment, thetemperature of the upper surface of the baffle plate 36, that of theupper surface of the feed melt 35 and that of the upper surface of aliquid sealing agent 40 can be measured at the same time.

What is claimed is:
 1. A method of growing a single crystal comprisingpulling a single crystal from a feed melt contained in a crucible undera high pressure inert gas atmosphere, covering the surface of the feedmelt with a liquid sealing agent, floating an unperforated baffle platehaving an outside diameter somewhat smaller than the inside diameter ofthe crucible in a predetermined position below the surface of the feedmelt to define a spacing between the baffle plate and the surface of thefeed melt and to define a gap between outside and inner peripheries ofthe baffle plate and the crucible, respectively, controlling the spacingbetween said baffle plate and the surface of the feed melt so that saidspacing is maintained at a predetermined spacing during pulling of thesingle crystal, causing relative rotation between the baffle plate andthe crucible, the periphery of the baffle plate including a feed meltguiding portion which causes movement of the feed melt from below thebaffle plate smoothly upward through the gap between the relativelyrotating baffle plate and the crucible to a solid-melt interface regionabove the baffle plate, heating discrete vertically spaced points in thefeed melt preselectedly and controlling the heat applied to saiddiscrete vertically spaced points in the feed melt.
 2. A method ofgrowing a single crystal according to claim 1, wherein said baffle plateis made from a material selected from the group consisting of Al₂ O₃,Si₃ N₄, BN and PBN.
 3. A method of growing a single crystal according toclaim 1, wherein said baffle plate is controllably located in the feedmelt by being pressed down from above through control rods by a forceequal to that necessary to counterbalance the bouyancy of said baffleplate and maintain same at the predetermined spacing from the surface ofthe feed melt as the crystal is grown.
 4. A method of growing a singlecrystal according to claim 1, wherein said baffle plate is fixed to acontrol rod which is suspended vertically axially movably from above thecrucible.
 5. A method of growing a single crystal according to claim 1,further wherein the crucible is moved to maintain the predeterminedposition of said baffle plate in the crucible during pulling of thesingle crystal.